Molecular-based diagnostics techniques capable of obtaining simultaneous multiple fluid properties such as temperature, density and velocity are critically important for characterizing the flows within airbreathing engines, such as scramjet engines and scramjet-turbine combined cycle engines for hypervelocity vehicles. At the other end of the velocity range, such techniques are needed to help in the development of the next generation of subsonic, low noise aircraft. Statistical correlations between these properties will lead to a more detailed understanding of the complex flow behavior as well as aid in the development of new turbulence models for scramjet engine flow path designs, and more accurate aircraft noise prediction tools. Required are instantaneous and simultaneous measurements of temperature, velocity, density, pressure, and chemical composition at multiple points in a gas when the spatial (hundreds of microns or less) and temporal (hundreds of nanoseconds or less) scales of the turbulent fluctuations are resolved. Specifically of interest are the mean properties and their turbulent variances and co-variances as well as the probability density functions. To date, diagnostics techniques to meet all these requirements on a single platform do not exist, but many linear and non-linear optical techniques are available for partial achievement of this goal. One of these linear techniques, the Interferometric Rayleigh Scattering technique (IRS) (discussed in Bivolaru, D., Danehy, P. M., Gaffney, Jr. R. L., and Cutler, A. D., “Direct-View Multi-Point Two-Component Interferometric Rayleigh Scattering Velocimeter,” AIAA-2008-0236, 46th Aerospace Sciences Meeting, Reno, Nev., Jan. 9-12, 2008), has been used for low-as well as for high-speed supersonic/hypersonic non-reacting and combusting flows yielding temporally and spatially resolved simultaneous measurements of two-components of bulk velocity.
Recent efforts have attempted to obtain the ro-vibrational temperature, and the species content of N2 and O2 from measurements with CARS (coherent anti-Stokes Raman spectroscopy), simultaneously with velocity with IRS. Those efforts include Danehy, P. M., Magnotti, G., Bivolaru, D., Tedder, S., and Cutler, A. D., “Simultaneous Temperature and Velocity Measurements in a Large-scale, Supersonic, Heated Jet,” Paper 1193, 55th JANNAF Propulsion Meeting, Boston, Mass., May 12-16, 2008. Also, Bivolaru, D., Lee, J. W., Jones, S. B., Tedder, S., Danehy, P. M., Weikl, M. C., Magnotti, G., and Cutler, A. D., “Mobile Rayleigh—CARS Instrument for Simultaneous Spectroscopic Measurement of Multiple Properties in Gaseous Flows,” 22nd International Congress on Instrumentation in Aerospace Simulations Facilities (ICIASF), Monterey, Calif., June, 2007; and Bivolaru, D, Danehy, P. M., Grinstead, K. D., Jr., Tedder, S., and Cutler, A. D., “Simultaneous CARS and Interferometric Rayleigh Scattering,” AIAA-2006-2968, 25th AIAA Aerodynamic Measurement Technology and Ground Testing Conference, San Francisco, Calif., Jun. 5-8, 2006. However, this work needs improvements in instrument precision, as well as additional simultaneous measurements, the gas density and a measurement of translational temperature from IRS.